From b4cf37ce1d32bc251d77bfa2976324946354202c Mon Sep 17 00:00:00 2001 From: Andres Freund Date: Sun, 26 Jan 2025 14:10:58 -0500 Subject: [PATCH v1 1/3] Move MAX_BACKENDS to pg_config_manual.h MAX_BACKENDS influences many things besides postmaster. I just noticed that we don't have static assertions ensuring BUF_REFCOUNT_MASK is big enough for MAX_BACKENDS, adding them would require including postmaster.h in buf_internals.h which doesn't seem right. Discussion: https://postgr.es/m/wptizm4qt6yikgm2pt52xzyv6ycmqiutloyvypvmagn7xvqkce@d4xuv3mylpg4 --- src/include/pg_config_manual.h | 12 ++++++++++++ src/include/postmaster/postmaster.h | 12 ------------ src/backend/storage/lmgr/lwlock.c | 1 - src/backend/utils/adt/xid8funcs.c | 1 - 4 files changed, 12 insertions(+), 14 deletions(-) diff --git a/src/include/pg_config_manual.h b/src/include/pg_config_manual.h index 449e50bd78c..9874302946e 100644 --- a/src/include/pg_config_manual.h +++ b/src/include/pg_config_manual.h @@ -42,6 +42,18 @@ */ #define FUNC_MAX_ARGS 100 +/* + * Note: MAX_BACKENDS is limited to 2^18-1 because that's the width reserved + * for buffer references in buf_internals.h. This limitation could be lifted + * by using a 64bit state; but it's unlikely to be worthwhile as 2^18-1 + * backends exceed currently realistic configurations. Even if that limitation + * were removed, we still could not a) exceed 2^23-1 because inval.c stores + * the ProcNumber as a 3-byte signed integer, b) INT_MAX/4 because some places + * compute 4*MaxBackends without any overflow check. This is rechecked in the + * relevant GUC check hooks and in RegisterBackgroundWorker(). + */ +#define MAX_BACKENDS 0x3FFFF + /* * When creating a product derived from PostgreSQL with changes that cause * incompatibilities for loadable modules, it is recommended to change this diff --git a/src/include/postmaster/postmaster.h b/src/include/postmaster/postmaster.h index 188a06e2379..e12af62a370 100644 --- a/src/include/postmaster/postmaster.h +++ b/src/include/postmaster/postmaster.h @@ -126,18 +126,6 @@ extern PMChild *AllocDeadEndChild(void); extern bool ReleasePostmasterChildSlot(PMChild *pmchild); extern PMChild *FindPostmasterChildByPid(int pid); -/* - * Note: MAX_BACKENDS is limited to 2^18-1 because that's the width reserved - * for buffer references in buf_internals.h. This limitation could be lifted - * by using a 64bit state; but it's unlikely to be worthwhile as 2^18-1 - * backends exceed currently realistic configurations. Even if that limitation - * were removed, we still could not a) exceed 2^23-1 because inval.c stores - * the ProcNumber as a 3-byte signed integer, b) INT_MAX/4 because some places - * compute 4*MaxBackends without any overflow check. This is rechecked in the - * relevant GUC check hooks and in RegisterBackgroundWorker(). - */ -#define MAX_BACKENDS 0x3FFFF - /* * These values correspond to the special must-be-first options for dispatching * to various subprograms. parse_dispatch_option() can be used to convert an diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c index 2f558ffea14..328b1bab659 100644 --- a/src/backend/storage/lmgr/lwlock.c +++ b/src/backend/storage/lmgr/lwlock.c @@ -80,7 +80,6 @@ #include "pg_trace.h" #include "pgstat.h" #include "port/pg_bitutils.h" -#include "postmaster/postmaster.h" #include "storage/proc.h" #include "storage/proclist.h" #include "storage/spin.h" diff --git a/src/backend/utils/adt/xid8funcs.c b/src/backend/utils/adt/xid8funcs.c index 20b28b2528c..d505e3fcf57 100644 --- a/src/backend/utils/adt/xid8funcs.c +++ b/src/backend/utils/adt/xid8funcs.c @@ -32,7 +32,6 @@ #include "lib/qunique.h" #include "libpq/pqformat.h" #include "miscadmin.h" -#include "postmaster/postmaster.h" #include "storage/lwlock.h" #include "storage/procarray.h" #include "utils/builtins.h" -- 2.48.1.76.g4e746b1a31.dirty